Manipulation of the immune response to adjuvant has long been utilized as an effective technique to enhance antibody production to soluble antigens. However, until recently, little has been understood about the effect of adjuvant on specific lymphocyte functions and interactions. The research covered in this grant was designed to assess the effect of adjuvant on distinct lymphocyte functions. Specifically, cytolytic T cell responses to tumors, helper T cell collaboration with B cells and suppressor T cell interaction with both helper and cytolytic T cell subsets are being evaluated. Studies on the effect of adjuvant on T cell function have shown that adjuvant stimulated suppressor T cell activity which regulated cytolytic but not helper T cell function. Furthermore, suppressor T cell activity was detect initially in the thymus and subsequently in splenic T cell populations, suggesting that the thymus was required for suppressor T cell induction. In testing this hypothesis, it was found that thymectomy prior to adjuvant prevented the induction of suppressor cells. Applying these findings to a syngeneic tumor system has shown that thymectomy prior to inoculation of mice with tumor virus prevented the late or secondary induction of reticulum cell sarcomas. Concomitantly, thymectomy resulted in the enhanced generation of cytolytic T cells directed against syngeneic tumor cells bearing the appropriate cell surface determinants. This work suggests that the primary role of the thymus in adult life may be regulation of mature T cell subsets by the export of inducible suppressor cells.